Process for preparation of dehydrated food products



June 14, 1949. w, W

PROCESS FOR PREPARATION OF DEHYDRATED FOOD PRODUCTS Filed Dec. 2, 1947 Illl||||||||||......|

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INVENTOR Patented June 14, 1949 OFFECE PROCESS FOR PREPARATION OF DEHY- DRATED FOOD PRODUCTS Wells Alan Webb, San Jose, Calif. Application December 2, 1947, Serial No. 789,211

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This is a continuation in part or my applica= tion Serial No.439,384 filed April 17, 1942, now abandoned, which was a division of application Serial No. 258,452 filed February 25, 1939, now Patent 2,283,302, May 19, 1942-.

The present invention relates to preparation oi food compositions by rendering certainiood substances porous and rigid by dehydration in liquid media and to the impregnation of the pores oi. such rigid food substances to produce edible products suitable for incorporation into confections, cakes, ices, and like products.

An object of the invention is to provide a novel method for dehydration of fruit and other foods.

Another object of the invention is to provide a method whereby the moisture absorbing capacity of dehydrated porous foods may be reduced or eliminated.

Another object of the invention is to provide a method enabling liquid fats or other fluids to be injected into the pores and cells of pufied fruits,

pufied grains and other porous food articles, thereby to increase the nutritional content of said foods.

Another object of the invention is to provide a method or covering the outer surfaces of particles of dehydrated fruit with a protective me-= dium, thereby to prevent absorption of moisture and adhesion of adjacent particles to one another.

A further object is to provide a number of new and delicious food compositions, comprising ices, cakes, confections and like food containing impregnated fruit.

Another object of the present invention is to provide a process for producing a substantially dehydrated fruit having a pufied or distended structure whereby the fruit is approximated.

The invention has other objects which with the foregoing will be set forth with the description of the preferred forms of the invention. It is to beunderstood, however, that I do not limit myself to said description, as I may adopt variations from said forms within the scope of the invention as set forth in the claims.

In my patent No. 2,110,184, issued March 8, 1938, I disclosed a method for pumng and dehydrating fruit whereby crisp, distended whole pieces or particles of fruit may be produced. Fruit produced by said method possesses the disactual appearance of the advantage of being hygroscopic to the extent that Q in a normal atmosphere it will absorb in a few to destroy all crispness; prevents such fruit from hours sufflcient moisture This hygroscopic quality former process.

2 remaining crisp or flrm when incorporated into ices, cakes and like prepared foods.

In the process referred to in the preceding paragraph, dehydration takes place in a vacuum. The absence of substantial concentration of any gaseousmedlum from the processing chamber makes it necessary for the heat required for the evaporation of moisture from the fruit to be transmitted to the fruit chiefly by means of radiant heat waves emanating from heated surfaces located adjacent to the fruit. Thus-the surfaces of the fruit which are directly exposed to the heat waves emanating from the heated surfaces are liable overheating or charring, whereas simultaneously the hidden portions or surfaces not exposed-t0 direct heat emanations v medium and reduced pressure, fruit or other food' may be rapidly and satisfactorily dehydrated .in deep layers and under reduced pressure without causing substantial decomposition of the fruit sugar. By my new method, heat is applied to all portions of the food by means of a heated edible liquid such as an edible fat, liquid petrolatum or other odorless, tasteless hydrocarbon oil of such a nature that its consumption by humans is not objectionable, glycerine, lecithin, liquid sugars such as corn syrup or other suitable medium; the liquid should have a vapor pressure sufficiently low that water can be rapidly removed from the fruit. The liquid medium is cycled successively through an external heater, and through the food being dehydrated. The external heater may include a still or settling tank to remove water contained in said liquid medium.

I have also found that fruit, or other food, may be puffed without interrupting and thuslengthening the drying period through the temporary increase in pressure that was necessary by my To accomplish puffing during some portion of the drying period, I now momentarily increase the temperature of the liquid medium flowing over the food. By raising the temperature of the liquid medium, I cause the rate of evaporation of moisture from within the food to increase to such an extent that the vapors in- 3 fiate or puii the particles oi! food in the course of their escape therefrom. During this step the vapor pressure within the processing chamber may remain at a practically constant reduced value which is substantially less than the vapor pressure of the heated fruit, and drying will therefore continue without interruption through every phase of the pulling operation.

The presence of a circulating liquid medium in contact with the food has the further advantage that, following pufling and dehydration, the food may be rapidly and completely cooled by quickly lowering the temperature of the circulating liquid medium.

The initial operations of my new process comprise therefore, the steps of partially dehydrating a food in contact with a circulating liquid medium and under reduced pressure, pulling the food under a constant reduced pressure by increasing the temperature or the liquid medium-and continulng the dehydration at reduced temperature until the food is substantially tree of moisture.

If at the termination of this last mentioned stage of dehydration, the liquid medium is cooled and then drained away from the food prior to the restoration of normal pressure to the inside of the drying chamber, then such restoration of pressure will drive air or other gas into the expanded cells and pores of the food. The product resulting from such a sequence of operations is a puffed food containing air in its pores and carrying on its exterior a thin coating of the liquid medium. This coating may be beneficial; for example, particles of fruit puffed in the above described manner by means of a liquid are delivered from the pufiing process with a protective coating of the liquid. This coating not only increases he nutritional value of the fruit, but it also retards absorption of moisture from the atmosphere, and materially reduces the tendency of adjacent particles to cake" or stick together. The thickness of this protective coating is increased by lowering the temperature of the liquid in contact with the fruit just prior to draining the fat away. The thickness of the protective coating is decreased by cooling as little as possible and draining away the liquid at as high a temperature as possible while imparting to the fruit st-mcient rigidity from the cooling step to enable the fruit to withstand the application of atmospheric pressure without materially losing its puffed structure. The thickness of the protective coating is further decreased by allowing a longer time Beriod for draining and before application of atmospheric pressure.

The liquid adhering to the surface of the fruit after draining is driven into the outer layer of fruit by application of atmospheric or superatmospheric pressure. In the case of certain fruits such as puffed Newtown Pippin apple slices, increasing the pressure well above atmospheric pressure to say 10 or 25 pounds per square inch gage, after the slices have been thoroughly cooled, serves to drive the liquid more completely into the pores. The result of such treatment is that the outer pores may become more or less completely impregnated. In storage, a liquid such as an oil or fat will often difiuse from the outer pores inward and the result then is an apple slice in which most of the cells are partially filled or coated with the oil and few are completely filled. For pie apples, a fat content of from 5% to 35% is considered acceptable. The pores of the apple are then only partially filled with fat while the balance of the space is air filled. A pie made from such an apple is not excessively rich, though it contains suilicient fat in the fill to give desired richness.

The termination of the last stage of dehydration may. on the other hand, be characterized by the continued presence of the cooled circulating liquid about and over the food. In such case, restoration of normal pressure serves to drive the liquid into the cells and pores of the food. The result is the full-cell impregnation of the food. For example, the cells of fruit particles pulled and dehydrated in contact with a fat become filled with fat if normal pressure is restored while the fruit remains submerged. Impregnation is, of course, improved by application of pressures above atmospheric to the covered fruit. Such full-cell impregnation may result in a fruit containing from 50% to 60% of fat, depending upon the degree to which the fruit has been puffed. The more fully impregnated product is suitable as a confection, as an ingredient of cakes and frozen desserts.

The characteristic that determines whether or not a fruit will pufi resides in the ability of the fruit to form cells or pockets large or small that containthe water vapor and from which the vapor slowly leaks during dehydration. Weakly made fruit flesh like that of watermelon cannot contain the evolving vapors and hence does not pull. Grapes with tough skins but without strong internal structures or membranes are puffed because the skin contains the water vapor. Dates. figs and prunes are additional examples of fruits that puff roundly in the whole condition owing to the presence of a tough skin.

Briefly summarized, the process of this invention includes lowering the pressure on the fruit while the fruit is at an elevated temperature to facilitate moisture removal from the fruit. Since the fruits with which the present invention is particularly concerned, e. g. those having a relatively fine cell structure of a microscopic nature such as raisins, apples, pears, bananas, peaches, apricots, prunes, dates and nectarines, include fruit sugars which are altered by heat, it is essential that the fruit not be held at a temperature whereat these alter undesirably for a time sufllcient to the undesirable alteration. Generally such fruit sugars caramelize at temperatures in the range of -200 F.; if subject to a temperature in this range for any extended period of time, the sugars may form undesirable products and may even char. This characteristic is more pronounced in some fruits than others; for example, pufied apple slices may be colored slightly brown, to a pale yellow or to a golden color by prolongation of heat during the pufiing and dehydrating process. Such slices, while unimpaired as to taste, have become chemically changed to the extent that, when the slices are incorporated into pie as apple pie fill, the slices, after cooking and cooling in the pie, become markedly darkened. -0n the other hand, apple slices processed by the very low absolute pressure and lower temperatures of my process are not materially darkened and produce a pie fill of exceptionally light and natural color. Similarly Thompson seedless grapes and other grapes of high sugar content, delicate flavor and color are puffed and dehydrated without materially increasing or deepening the natural color; these fruits produce a very light colored pie fill, much preferred to darker colored fills. Generally, one

should employ a reduced pressure of the order of a vacuum equivalent to a half pound pressure aware:

absolute and preferably even less, of the order of a quarter of a pound absolute. At three quarters of a pound absolute, it is necessary to employ such an elevated temperature that undesirable heat alteration and even charring of the fruit sugars occur. High pressures of the order of four pounds per square inch are entirely undesirable.

Direct contact of the fruit with the dehydrating and heat conducting liquid enables an extremely rapid rate of dehydration to be obtained; for example, apples ordinarily requiring 8 to 15 hours for dehydration in ordinary drying kilns where .air is the dehydrating and heat conducting medium can be completely dehydrated from the fresh state to less than 2% moisture content in my process employing heated oil and vacuum, the time required beingtwo hours or less depending upon the thickness of the slices.

The use of a low pressure with rapid heat transfer permits apples and other fruits to be rapidly dehydrated without danger of oxidase-catalysed browning; therefore, no sulfur dioxide or other bleaching means is required. Because oxygen is excluded by covering the fruit with a liquid, and oxygen already in the fruit is removed therefrom by escaping water vapor; browning of the fruit is prevented during dehydration. I

The heating of the fruit under reduced pressure enables the fruit to be dehydrated to a moisture content of 6% by weight and less; I prefer to reduce the moisture content to 2% by weight and even less; heat exchange is facilitated and simplified by utilizing a suitably heated liquid of low vapor pressure. During the heat-, ing the pressure is preferably gradually reduced so that the greatest vacuum is applied to the driest fruit. In this way, the best utilization of the low pressure is secured. Because of the cooling of the fruit due to moisture evaporation, the fruit usually does not attain the temperature of heating liquid. If during the dehydration, the temperature of the heat exchange liquid is elevated for a short period, pufiing and extending of the fruit cell structure is effected.

If, after the desired degree of dehydration has been attained, the fruit is cooled while the reduced pressure is maintained untfl the fruit has attained a temperature approximating atmospheric temperatures of the order of 68 F.-90 F., the puffed, distended condition of the fruit is maintained; if the pressure is returned to atmospheric before the fruithas attained sufiicient rigidity, the cell structure collapses, the fruit density is relatively high, but it is so dehydrated as to be relatively stable and resistant to mold and the like.

Summarizing: The fruit initially processed can be in a natural condition or it can be partially dehydrated as by sun drying or kiln drying to reduce the moisture content to some extent. The process briefly comprises subjecting fruit to a reduced pressure of the order of a half pound pressure absolute or less and to a temperature of '70-100 0., usually only for a period of from 10 to 60 minutes, until the fruit contains 6% or less of water. Preferably during the dehydration, the pressure is reduced gradually to about 0.1 pound per square inch absolute to make maximum economic utilization of the application of the low pressure. If, during the dehydration, the temperature'is increased for a minute or two to about 00-l25 C., the fruit will be further extended and the product will have a desired puffed appearance. After the dehydration, the pres- IOQI have mentioned. Materials having a coarse,

, allow the trays of fruit to be sure can be released while the heat exchange medium, e. g. the liquid, is in contact with the fruit so that the puffed or unpufled fruit is impregnated therewith or with a gas admitted for this purpose.

The invention is particularly applicable to any fruit or like substance having a membranous cell structure capable of forming water vapor retaining pockets or cavities such as those fruits which non-membranous cell structure and of a fibrous nature such as melons-cannot be puffed or distended although they can be dehydrated;

The practice of the process of this invention will become further apparent upon consideration of a presently preferred embodiment illustrative of one form'of the invention.

I prefer to carry out my process in an apparatusof the form shown in the accompanying drawings, which are a part of the specifications of the present invention. With reference to the drawings:

Figure 1 shows the general arrangement of apparatus with vessels shown'in vertical half section, and the trays shown in section A-A of Figure 2.

Figure 2 is a plan view of the processing chamber taken through section 6-0 of Figure 1.

, Figure 3 is a view of one of the trays taken through section BB of Figure 2.

With reference. to Figure 1, the processing chamber is composed 4 and trays 5. The processing chamber is connected by means of inlet pipe I3 and outlet pipe II to cooling chamber 2, heating-chambers 3 and 3a and supply tank 8. p extends into the base of the processing chamber and serves to connect through vacuum pump. Cap I6 prevents splashes of oil from entering the vacuum line. By means of hook 2|, cover I may be lifted from base 4 to emoved. The parting between cover I and base 4 occurs at a sealing junction 6. Trays 5 are supported on brackets 23 attached to upright panels 24 and 25. Panels 24 and 25 are attached at their lower end to bottom 20 of base 4 and at their upper end, the two panels are fastened to each other by means of cross brace 26.

A manifold 22 connects-with the inlet pipe l3 and extends upwardly through the processing chamber. Outlets are provided in the manifold at locations suitable for the discharge of liquid into the trays. Liquid from outlets 21 passes through the trays and is discharged from the right-hand side of the trays into troughs 28. From 28, the liquid passes through suitable openings in panel 25 and drops to base 4 where it collects in bottom 20 and passes out through pipe I4. A liquid level gage l9 indicates the level of liquid remaining in bottom 20.

The trays 5 containing the food to be dehydrated are of special construction to permit proper circulation of the liquid through the food, and to permit the liquid to be drained from the food before the trays are removed from the processing chamber. Each of the trays contains a grid 29 on which is laid a screen 30 to hold the food 32. Over the food is a second screen 3| fastened to the tray by a bracket that permits in part of cover I, base valve H with a aware level of 33a, and simultaneously to maintain the m liquid level above screen 31 by causing it to flow over the upper edge 35a of bailie 85.

when it is desired to drain substantially all of the liquid from the trays, a valve mechanism is utilized. This mechanism is constructed as follows: A rod 31 having a handle 38, a gland 50 and bearing 39 are provided. Rigidly mounted on rod 31 and engaging with valves 40 are tap pets 4!.

An upward push on handle 38 causes the ends 41a of tappets 41 to engage and raise valves 40, so permitting liquid from the trays to drain into troughs 28. A downward pull on the handle lowers the tappets and allows the valves to close under the impulse of valves springs 55. Gland 50 prevents leakage of air into the chamber.

Chambers 2, 3, 3a and 8 are provided with heat transfer coils l0, H, Ho and l 2 respectively. I shall now describe a typical application of my new process, making use of the preferred form of apparatus as described in the preceding paragraphs. For example: By means of fluid of suitable temperature flowing through the heat transfer coils for the respective chambers, the

liquids in chambers 3 and 8 are maintained at from 70 C. to 100 C., the liquid in chamber 3a is maintained at from 100 to 125 C., and liquid in chamber 2 is maintained below 60 C. Sun

dried apples containing about 20% moisture are cut into particles and placed in the trays. The

trays are slid on the racks into the processing chamber, and cover I is lowered to form a seal. Thereupon the chamber is evacuated to about 0.75 pounds per square inch absolute by suitable evacuating means connected to valve II. A liquid at 70 C, to 100 C. from heater 3 passes through valve 44 and is circulated approximately ten minutes through pipe 13, manifold 22, out of orifices 21 and through the fruit by means of pump 15.

Evaporation of moisture takes place; the vapor'50 rises through screens 3| and is drawn on through pipe l5. Cool fat from the bottom of the trays overflows bafile 35a and passes to the bottom of the chamber to be recirculated by pump 15 through heater 3. Thermometer 42 indicates the temperature of the outgoing liquid. A similar thermometer may be installed on pipe l3 to indicate the temperature of the incoming liquid. The temperature of the fruit may be recorded by inserting suitable wire thermocouples into particles of fruit and leading the wires to a potentiometer outside of the chamber. To complete the dehydration and 'to puff the apples, valves 44 and 45 are closed, and valves 48 and 41 are opened to permit fat at a temperature of from 100 C. to 125 C. from chamber 3a to pass over the apples. This displaces the cooler liquid already covering the fruit, and increases the rate of evaporation sufliciently to inflate the apple particles by the rapid generation of vapor within the particles. If liquid at about 115 C. is in contact with the fruit for a period of not more than one or two ininutes, pulling without material decomposition of the fruit sugars takes place. Then valves 46 and 41 are closed and cooler liquid is voil is circulating through this chamber. valve 40 may be opened momentarily. The fruit is then quickly cooled by admitting other cold liquid at 20 C. ,to 40 C. which is admitted to the trays by closing valve I and opening valves 40 and 50 to admit into line It the liquid in cooler 2. This liquid displaces the hot fat in the trays and cools the fruit. The dehydrated fruit should be cooled to a temperature whereat it is rigid; when the fruit contains 6% moisture, one should generally cool to about 50 R; at a lesser moisture content,

7 the cooling oil can be at a higher temperature and on fruit containing only 2% moisture I have successfully used oil at F.

After allowing several minutes for that amount of cooling to occur that is required to give the fruit structural rigidity, the cool liquid may be injected into its pores and cells by slowly admitting air at normal atmospheric pressure into the processing chamber while the liquid still covers the fruit. Or, if it is desired to produce air-filled fruit, this may be accomplished by stopping the circulation of cool liquid, pushing upward on handle 38 to drain the liquid and, when the trays are drained, slowly admitting air to the chamber by opening valve l8.

While filling the cells and pores of a food with a liquid medium, it is essential to maintain the level of the liquid over the fruit. If absorption of liquid occurs more rapidly than the liquid is supplied by spouts 21, then the level of the liquid is liable to fall below screen, and portions of the food become exposed tothe air. These portions would then become filled with air instead of liquid. To aid in preserving the liquid level above screen 3|, a suitable level indicator or sight glasses in cover 1 may be installed which will enable the operator to determine the level in each tray. The operator will then admit air by regulating valve l8 in such a manner as to increase the air pressure sufficient to drive liquid into the fruit at a rate not exceeding that at which liquid is supplied by spouts 21.

Owing to the rapid evaporation of water from the fruit, the fruit temperature is maintained substantially below the temperature of the heating liquid. By means of thermocouples inserted into the interior of pieces of fruit, I have found that the fruit does not rise above F. initially, even though the temperature of the heating liquid in contact with the fruit is higher by 100 F. By employing a very rapid circulation of hot liquid over the fruit particles, an extremely rapid rate of water evaporation may be maintained until the fruit juices are concentrated and the fruit temperature has risen to approximately a carameiizing temperature of F. At this moment, the temperature of the liquid in contact with the fruit must be sharply reduced to 200 F. or lower, even to 180 F. in order to avoid overheating and caramelizing the fruit; dehydration proceeds at decreasing pressure until substantial dryness (2% or less) is achieved.

Rapid evaporation of moisture is suited to the manufacture of fruit products not requiring subsequent cooking such as dehydrated apple chips;

this product resembles potato chips, being made from apple slices about one eighth of an inch or one sixteenth of an inch or less in thickness. However, for other products such as pulled grapes or pufl'ed apple for pics, a certain overpumng or bloating is liable to result from extremely rapid evaporation; also, surface caramelization may result. the fruit surface being discolored without the interior being affected. Therefore, I prefer, when manufacturing the dried fruit products for the latter use, to limit the period when the liquid in contact with the fruit is at a temperature substantially above the caramelizing temperature. For example, I prefer to process fruit according to the following specific examples, although itv is understood that I am not limited thereby except as set forth in the claims appended hereto.

Example 1 Eight hundred forty pounds of Gravenstein dried apples, containing 22% of moisture and 1000 part per million of sulfur dioxide, were placed in a container upon which a vacuumwas drawn to produce an absolute pressure within the flask of 0.75 pounds per square inch. Heated ooconut oil at 234 F. was admitted to the vacuum container while vapors were continuously being removed by means of a suitable low temperature condenser and vacuum pump. The process was continued according to the following tabulation:

Ah 1 1 Elapsed pre sin P53??? ltounds kpproxirnate W8 V 111 minutes $221321 fl k 16501 25" 01 31 13? F abs. o .74 an 0 05 I 1 .es 170 17.0 111 3 .49 17s 2111 120 5 .37 184 29.5 198 1 .34 200 24.0 100 I 9 .21 198 1.5 110 11 .18 200 14.9 175 13 .15 199 13.1 177 15 .12 198 9.9 178 I 11 .11 190 7.96 179 19 .09 190 5.50 180 21 .09 190 5.56 180 as .09 194 5.50 181 In the first minute of operation of the process, the hot oil was cooled rapidly by the cold metal of the vacuum container and by the cold fruit. This accounts for the lower rate of water vapor the rate for the second and subsequent minutes. In 23 minutes of operation a total 01' 173 pounds of water vapor were removed under absolute pressure conditions ranging from 0.74 initially to 0.09 pounds per square inch absolute at the end of the process.

At the conclusion of the evaporation, the liquid was drained from the fruit and cool cottonseed oil at less than 68 F. was admitted to circulate through the fruit and cool the slices to rigidity. Finally, the cool oil was drained away and air was admitted to the chamber. The product was a puffed crisp apple containing oil in the outermost layer of the pores of each slice. The moisture content of the apple was reduced from 20% to 1.5% and the sulfur dioxide from 1000 parts per million to approximately 100 parts. The total oil content was found by analysis to be 9.4%.

In some cases the final oil content may be higher, e. g. 15% to 20% depending upon the porosity of the particular apples and the speed with which the process is carried out. I have found that rapid dehydration causes a casehard- Emmple 2 Fresh Newtown Pippin apples were peeled and red and then sliced to approximately 1'; inch thickness. The slices containing about 84% moisture were immersed in 3% salt-65% sugar minute and were then placed in Absolute pres- After 104 minutes had elapsed the fruit slices were cooled with 0001 oil, air was let into the chamber to atmospheric pres sure. The apple chips resembled potato chips;

they werea pure white. crisp and delicious to 3 taste. possessing unimpaired apple flavor and less than 2% moisture.

Example 3 Fresh Thompson Seedless grapes were cleaned of stems and placed in the vacuum vessel which was evacuated. Heated coconut. oil was admitted and the treatment was carried out as tabulated:

tercondenser; air and The processed Thompson seedless grapes were fully pufied. crisp and had retained their original yellow-green color.

In order to produce a vacuum inexpensively, I prefer to utilize a vacuum system comprising a first stage booster ejector, which discharges into a booster condenser; air and water vapor not condensed by the latter are compressed by a second stage ejector that discharges into an inby the intercondenser atmospheric pressure phere by a third stage ejector.

It is a characteristic are further compressed to will handle large quantities of water-vapor at' pressure, the cost of operation being not materially greater than when it is operating to'handle smaller quantities of the oil was drained and Elapsed Absolute prestPgOOBSSilgg oil tApprox imate sure poun s per mpera ure, empera ure 0 minutes square inch F. fruit, F.

water vapor not condensed and elected to the atmosthe desired dehydration 11 water vapor at relatively low absolute pressure.

To obtain a continuous reduction in pressure on the fruit during the evaporation, it is essential that one utilize a batch process. JElgwever, may be obtained in a continuous process in which the fruit is continuously in ected and removed from the chamber as in Hutteman Patent 1.929.691, providing the lowest absolute pressure required by the process is always maintained in the chamber.

In the present invention I may utilize not only whole or relatively large out particles of fruit, but also comminuted fruit as fruit cakes which may be rap dly dehydrated and pufled by contact with a liquid at reduced pressures, according to the process described above, without causing substantial decomposition of the fruit sugars. Furthermore, pulled products containing in their cells either a gas, a liquid or a solid, may be produced.

Foods may be impregnated with any of a wide variety of liquids by conducting the desired liquid into contact .with the food prior to the resto ration of normal pressure. Thus puffed fruits may be impregnated with aqueous syrups. with condensed milk. with melted milk chocolate, with eggs albumin, gelatin solutions, or other liquids, by draining away under reduced pressure the heating or cooling liquid that may be in contact with the fruit and covering the fruit with the desired impregnating liquid prior to the restoration of normal pressure. Some such liquids will coagulate after they have been injected into the fruit to form fruit im regnated with solids. For example, the acid of the fruit causes coagulation of milk solids, and of egg albumin to take pace shortly after milk or egg albumin has entered the cells of the fruit. Gelatine can be made to sol d fy and yru s c n be caused to crystallize by allowing time to elapse and by reducing the temperature after impregnation.

Full cell impregnation is not limited to foods that have been dehydrated in the manner described. It is possible by this invention to impregnate any food having a porous or cellular structure and possessing suilicient structural rigidity to prevent collapsing under pressure. For example, puffed grains may be impregnated. Fruit processed by the method oi my aforementioned United States Patent, namely No. 2,110 184, or other dehydrated fruits, fruit cakes or fruit powders may be evacuated of air and impregnated with fats or other liquids in the manner described in the preceding paragraphs.

It is known that dehydrated crisp fruits can be broken into particles of any desired size to produce granulated fruit and powdered fruit useful in baking. However, such products have the disadvantage that they tend to cake when stored or exposed to the atmosphere. When these products have caked. they are diflicult to use in baking. To overcome this difliculty, I place such granulated or powdered fruit'before caking into my new apparatus and impregnate them with a fat such as melted hydrogenated cottonseed oil. Thus, protected, ceptible to caking, and the resulting product can be mixed with flour in a manner similar to that used for ordinary shortening. Grain flour may be similarly impregnated with a fat to produce a. composition of flour and fat convenience for use in baking.

Following injection or impregnation of dehydrated foods with liquids containing water, or

other solvent such as alcohol, the solvent may be (6. pressure,

the mass-of fruit is not susremoved from the food by a further heating under reduced pressure. This process of alternate injections and drying may be repeated any number of times until all of the pores and cells oi the food are filled with a substance brought there throughthe medium of the solvent.

Many beneficial eflects can be achieved. For example, rennet dissolved in a solvent may be injected into a food, the solvent may then be evaporated, and sweetened condensed skim milk or whole milk may then be injected into the food at about 25 C. to 45 C. whereupon the milk solids would be coagulated. If desired, the food may then be used, for example in ice cream, or the food may be dried further, reiniected with rennet and the processrepeated until the food is filled with milk solids.

I have found that dehydrated food such as crisp fruit filled with a fat, with milk solids, or other substance, may be incorporated into frozen desserts such as ice cream, or it may be coated with a thick layer of fat or chocolate and incorporated into a frozen dessert without causing appreciable immediate loss of crispness or flavor. The result is a delicious cold dessert. Impregnated foods such as small crisp cookies may be similarly coated and/or impregnated to serve as confections, .or for incorporation into ice cream.

I have found that uncoated dehydrated fruit impregnated with a fat may likewise be incorporated into ice cream and can be kept for extended periods of time without complete loss of crispness.

To produce an, iced product that will remain uniform instorage, it is well to allow fat impregnated fruit to acquire moisture before it is incorporated into a frozen mixture such as ice cream. I have found that a convenient way to moisten the fruit is to sprinkle it gently with water, or expose it to a humid atmosphere, or submerge it in water momentarily.

Analternative method for producing a uniform iced roduct containing fat impregnated fruit is to allow the fruit time to attain equilibrium with the moisture in the iced product prior to consumption. Storing ice cream containing fat-impregnated fruit at a temperature of 5 to 10 C. for twenty-four to forty-eight hours will produce a product that will change but slightly when stored thereafter under the conditions customary for ice cream.

Fat impregnated fruit is useful in baking; in breads and cakes, the fat impregnated fruit retains its shape and firmness during cooking to a greater extent than dried fruit not impregnated.

I claim:

1. A process for dehydrating fruit comprising subjecting fruit to contact with an edible liquid of low vapor pressure at a temperature of 70- C. and to a reduced pressure of less than about one half pound per square inch absolute pressure to reduce the water content of the fruit to less than 6% by weight. momentarily increasing thetemperature oi the liquid to about 100- v C. while said fruit is subject to said reduced pressure to pull said fruit, and cooling the dehydrated fruit under substantially said reduced pressure to maintain the puffed condition in the fruit.

2. A process for dehydrating fruit comprising subjecting fruit to contact with an edible liquid of low vapor pressure at a temperature of 70- 100 C. and to a reduced pressure of less than about one half pound per square inch absolute gradually further decreasing the presof relatively low vapor sure on the fruit and liquid to about 0.1 pound per square inch absolute to reduce the water content of the fruit finally to about 2% by weight, momentarily increasing the temperature of the liquid to about 100 125 C. while said fruit is subject to said reduced pressure to pufi said fruit, and cooling the dehydrated fruit under substantially said reduced pressure to maintain a pufied condition in the fruit.

3. A process as in claim 1 wherein the dehydrated fruit is cooled to about atmospheric temperature and air is then admitted into contact with the fruit to impregnate the puffed fruit.

4. A process as in claim 2 wherein the dehydrated fruit is cooled to about atmospheric temperature and air is then admitted into contact with the fruit to impregnate the pufied fruit.

5. A' process for dehydrating fruit comprising subjecting fruit to contact with an edible liquid or relatively low vapor pressure and at a temperature of 70-100 0., maintaining a reduced pressure of less than about one half pound per square inch absolute pressure on' the fruit and liquid at said temperature for a time sufilcient to reduce the water content of the fruit to less than 6% by weight, and cooling the fruit to about atmospheric temperature.

6. A process for dehydrating fruit comprising subjecting fruit to contact with an edible liquid pressure and at a temperature of 70-100 0., and under a reduced pressure of less than about one half pound per.

square inch absolute pressure, gradually decreasing the pressure on the fruit and liquid to about 0.1 pound per square inch absolute to reduce the water content oi the fruit finally to about 2% by weight, and cooling the fruit to about atmospheric temperature.

.liquid is admitted into contact 7. A process for dehydrating fruit comprising subjecting fruit to contact with an edible liquid of relatively low vapor pressure and at a temperature of 70-100 C., maintaining a reduced pressure of less than about one half pound per square inch absolute pressure on the fruit and liquid at said temperature to reduce the water content of the fruit to less than 6% by weight, and cooling the dehydrated fruit under substantially said reduced pressure until the fruit is firm and rigid.

8. A process as in claim 1 wherein an edible liquid is admitted into contact with the fruit to impregnate the fruit as said reduced pressure is released to atmospheric.

9. A process as in claim 2 wherein an edible liquid is admitted into contact with the fruit to impregnate the fruit as said reduced pressure is released to atmospheric.

10. A process as in claim 7 wherein an edible with the fruit to impregnate the fruit as said reduced pressure is released to atmospheric.

WELLS ALAN WEBB.

REFERENCES CITED Theiollowing referenices are of record in the. file of this patent:

UNITED STATES PATENTS Number Name Date 1,035,838 Anderson Aug. 20, 1912 1,929,691 Hutteman Oct. 10, 1933 2,110,184 Webb Mar. 8, 1938 2,278,463 Musher Apr. 7, 1942 

